The transparent conductive film to be used as an electrode in a transparent touch panel is generally made of a metallic oxide such as ATO (antimony oxide/tin oxide), FTO (tin oxide/fluorine dope), ITO (indium oxide/tin oxide), FATO (antimony oxide/tin oxide/fluorine dope), or the like. Among others, the resistor-film analog type transparent touch panel is required to have a surface resistance of 200–2000 Ω/sq and be highly transparent and less colored.
The resistor-film analog type transparent touch panel has such a structure that a lower electrode substrate comprising an insulating substrate such as a glass plate or a film having on its surface a lower electrode made of a transparent conductive film and dot-like spacers, and an upper electrode substrate comprising an insulating substrate such as a film having on its surface an upper electrode made of a transparent conductive film are laminated. The transparent touch panel is thus enabled to make an input by pressing a portion of the surface of the transparent touch panel from the input surface side so that the two electrodes are put into contact and electrically conducting with each other.
The transparent conductive film formed in the transparent touch panel is normally formed by a physical film formation process such as evaporation process and sputtering process or a chemical vapor phase process such as CVD process. In these processes, the mean crystal grain size (R) within a plane observed at the film surface of the transparent conductive film is controllable. For example, in the case of a physical film formation process, the mainstream is transparent conductive films made of ITO, where the surface resistance value is required to be 200–2000 Ω/sq, rather higher as compared with electrodes for liquid crystal displays. However, because ITO is low in specific resistance, it is necessary to increase the surface resistance value by forming an ultrathin film having a film thickness of about 100–200 Å.
Under these circumstances, because the transparent conductive film is provided as an ultrathin ITO film, the mean crystal grain size (R) is as fine as 10–5 nm, where the arithmetic mean roughness (Ra) as observed by an atomic force microscope is as small as 0.1–0.3 nm and the root-mean-square roughness (Rms) is as small as 0.25 nm. For example, a surface cross-section of a transparent conductive film is formed generally triangular of grains as shown in FIG. 5 and FIGS. 17 to 19.
Accordingly, in a transparent touch panel using such transparent conductive films, because mutually contacting cross sections of transparent conductive films are formed generally triangular of grains, the so-called light touch input that an input state can be held for a slight-load input becomes unstable. Further, in the case of successive inputs with an about 10 g load by using a pen or the like, there would occur frequently line breaks of continuous lines and mis-input portions as shown by A in FIG. 6 such that proper inputs could not be obtained.
Thus, in order to solve these phenomena, such countermeasures as widening the spacer distance or reducing the spacer height could be conceived.
However, widening the spacer distance would make it more likely to occur that mis-inputs happen upon contact of the palm or other events.
Also, reducing the spacer height would cause the distance between opposing electrode substrates to be so short that Newton's rings due to light interference would occur between the transparent conductive films, degrading the visibility.
As a further countermeasure, it is also possible that the threshold voltage Evs (see FIG. 7) that conditions ON/OFF state upon an input by the transparent touch panel is set low, thereby compensating a voltage reduction due to contact resistance developed between opposing electrodes for an easier input. However, this would make it likely to occur that even unstable inputs are accepted so that coordinate jumps would frequently occur, as an issue. That is, as shown in FIG. 7, in the case where the threshold voltage Evs is set to a low one as a countermeasure for the phenomenon that the detected voltage Ev (see FIG. 4) fluctuates up and down due to variations in the contact resistance value Eb, for example, where the threshold voltage is set to 3.6 V, if there have been two-place inputs of 4.0 V and 3.5 V simultaneously, such as upon a film contact due to improper strain or upon a finger-and-pen simultaneous contact where a finger contacts a portion near a pen-contact portion at the same time as the pen contacts there, it is decided as a mis-input so that no display is given on the liquid crystal display screen or the like, where a case that there are no coordinate inputs at the relevant portion, i.e., line breaks result (see FIG. 6).
Accordingly, an object of the present invention is to provide a transparent conductive film for use in a transparent touch panel capable of performing stable, light touch inputs, a transparent touch panel using the transparent conductive film, and a method for fabricating a transparent conductive film, by which the above-described issues can be solved.